typos

rtsched-doc.tex

 \TaskInterval{i}{t1}{t2}{label}
 \end{verbatim}
 
-This command draws an horizontal double arrowhead for the \texttt{i}-th task from \texttt{t1} to \texttt{t2} with the specified \texttt{label} in the middle.
+This command draws an horizontal double-headed arrow for the \texttt{i}-th task from \texttt{t1} to \texttt{t2} with the specified \texttt{label} in the middle.
 
 \begin{figure}[!htbp]
   \centering